The invention presented herein relates to circuitry for automatic adjustment of the frequency of a clock generator used in the generation of data clock signals for a laser printer to compensate for variations in scanner frequency and data clock rates for a laser printer using a self-resonant scanner.
Self-resonant scanners can be used in a scanning system for a laser printer for providing line scans at an imaging receptor which receives the output from the laser. Since self-resonant scanners have a sinusoidal velocity, data clock signals are generated to correct for the sinusoidal velocity of the self-resonant scanner so that the desired potential on-off operations of the laser along a scan line of the imaging receptor will be at equally spaced intervals. In one such an arrangement, a first clock generator provides clock signals which are spaced by equal time intervals from which clock signals are selected that can be used to control the frequency of a second clock generator which provides the data clock pulses for use in supplying control data signals to the laser. Selection of clock pulses from the pulses provided by the first clock generator is controlled by a program stored in a programmable read only memory (PROM). The program is based in part on the sinusoidal variation in velocity of the scanner. The PROM is addressed by an address counter which receives the output of the first clock generator. The frequency of the self-resonant scanner can vary slightly which is objectionable since it causes variations between expected and actual beam velocity which, in turn, if not compensated for, will result in other than desired pixel spacing. In addition, the arrangement described also produces some undesirable variations in the frequency of the second clock generator which causes similar variations between expected and actual beam velocity which, in turn, if not compensated for, will result in errors in the pixel spacing.